Grinding diamond wheel, and method of making same

ABSTRACT

A diamond grinding wheel for forming the edges of glass plates into desired cross-sectional shapes wherein the diamond layer of the grinding wheel is a radial cross-section passing through the axis of said wheel and has continuously varying and uniform distributionof the diamond abrasive in accordance with grinding work required for shaping the edges of the plates to be ground and the method of manufacturing such a wheel. It is an object of the invention to prevent the uneven deterioration of the grinding surface of a pencil-edged diamond grinding wheel resulting from the grinding surface of the diamond layer of the wheels being deformed excessively from a given curvature radius in the process of grinding the cut edges of glass plates.

United States Patent Gomi [451 Aug. 20, 1974 GRINDING DIAMOND WHEEL, AND METHOD OF MAKING SAME Shoshichiro Gomi, No. 820 Chitose, Kawasaki, Kanagawa Prefecture, Japan Filed: Jan. 27, 1972 Appl. No.: 221,206

Related U.S. Application Data Continuation-impart of Ser. No. 868,518, Oct. 22, 1969, abandoned.

Inventor:

U.S. Cl. 51/206 R, 51/307. 425/130,

425/406 Int. Cl B24d 5/00, B24d 7/00, C04b 31/16 Field of Search 5 H206 R, 293, 307-309 References Cited UNITED STATES PATENTS l/1942 Kinney et al 51/206 R 10/1956 Robinson et al t 51/309 X 8/1965 Pratt 51/293 Primary Examiner-Othell M. Simpson Attorney, Agent, or FirmJohn J. Byrne; Edward E.

Dyson [5 7 1 ABSTRACT A diamond grinding wheel for forming the edges of glass plates into desired cross-sectional shapes wherein the diamond layer of the grinding wheel is a radial cross-section passing through the axis of said wheel and has continuously varying and uniform distributionof the diamond abrasive in accordance with grinding work required for shaping the edges of the plates to be ground and the method of manufacturing such a wheel.

It is an object of the invention to prevent the uneven deterioration of the grinding surface of a pencil-edged diamond grinding wheel resulting from the grinding surface of the diamond layer of the wheels being deformed excessively from a given curvature radius in the process of grinding the cut edges of glass plates.

2 Claims, 11 Drawing Figures GRINDING DIAMOND WHEEL, AND METHOD or MAKING SAME This is a continuation-impart application of my copending application Ser. No. 868,518, filed Oct. 22, 1969, now abandoned entitled GRINDING DIA- MOND WHEEL.

When prior grinding wheels are put to the grinding of the end faces of glass plates into desired contours, the configurationof their diamond layers gradually resembles the initialend face shape of the glass plate material to be ground. As aresult, the consequent increase in the radius ofthe'diamond layer is rendered virtually unusable'for. grindingwork until the curvature radius is corrected. Previousattemptsto lessen such deformation byincreasing the content of abrasive diamond grains. have been. unsuccessful. Although increasing hardness throughout: will certainly reduce deformation over a setspan of time, this-advantage is accompanied by additional costand an unacceptable heat generated inthe vicinity of a center portion of the cross section of the glass plate. Grinding speed is reduced because the glass willinot standfurther grindinguntil the temperature is-reduced.

Another objective of this invention is to provide a method of manufacturing a wheel havingthe aboveidentified advantages and characteristics.

These and other objects of the invention will become moreapparent to those skilled inthe art by reference to the followingdetailed description when viewed in light of the accompanying-drawings wherein:

FIG. 1 illustrates inzcross section a conventional pencil-edgeddiamond grinding wheel;

FIG. 2a portrays in .cross sectiona glass edge prior to grinding;

FIG. 2b portrays the edge of FIG. 2a after grinding;

FIG. 3 ilustrates a grinding layer formed in accordance with this invention;

FIG. 4 illustrates an alternate shaped grinding edge;

FIG. 5 plots characteristic curves showing the comparative results of testing of the grindingwheels made in accordance with the present invention;

FIG. 6a is s top plan of an'arrangement of diamond grain distribution;

FIG. 6b is a vertical cross-section of a diamond wheel having the dimensions of the wheel shown in FIG. 3; FIG. 7 is a diagrammatic perspective of a container for the grain distribution shown in FIG. 6; and

FIG. 8 isa diagrammatic perspective of apparatus for feedingthe contents of the container of FIG. 7 to a mold.

The following factors affect the hardness of a diamond grinding wheel;

a. the degree of contained abrasive diamond grains;

b. the strength and hardness of an employed wheel bond (the bonding agent for-the abrasive grains); and,

c. the conditions of grinding.

grinding the edge face of a-glass plate G into a given exemplary curvature radius such as that shown in FIG. 2b. It can be seen that the end sides of the glass plate must be ground by a quantity of machining height (a) while at the center portion B only a machining height (b) must be ground.

Since conventional wheels have uniform hardness throughout their abrasive layers, the amount of work done at A is a/b times that at B. Deformation of the layer will continue until the relation .a/b 1 is obtained. There is, equality in the machining ratio between the area A'and the area B suggests the linearity of the cross section of the diamond layer of the wheel. Any increase in hardness of a wheel for the .purpose of minimizing the deformation of its diamond layer results in increased cost and undesirable heat.

In accordance with this invention, the ratio of the grinding abrasive with respect to the bonding material is gradually increased from a minimum at B to a maximum at the side A. The bonding material is oftentimes brass or a substance of similar qualities. The increased concentration of diamond particles is illustrated by a higher density of black dots on the drawings. There fore, if increased variations in the rate of diamond content is given between A and B in proportion to the ratio of work to be done therebetween (or stated otherwise, with the ratio of consumption therebetween) the diamond layer is worn at a constant level of consumption and thus maintains the same cross-sectional shape thereof as at the beginning even though the amount of work done at the respective grinding areas A and B is different; The uniform wear of diamond layer contributes to increased grinding operations without repeated dressing and replacement. Consequently, by disposing a layer having a successively differing distributionof diamond particles in a cross section, the present invention enables continuous grinding work of a given shape determined so as to minimize the consumption of the diamond layer.

Although the foregoing explanation has been con fined to arcuate grinding work, the end faces of glass plates of any shape besides arcs, such asthe V-shape seen in FIG. 4. The FIG. 4 embodiment can grind exactly in accordance with their initial shapes by means of a wheel witha diamond layer having gradual variation in diamond content in proportion with grinding work done for the end faces.

In accordance with the foregoing, tests were made I under the conditions as given in the Table below. The

Of the above three mostintluential elements, assumtest results are graphically represented by the curves of FIG. 4.

In FIG. 5 curve 21 represents the result of the first test, curve 22 the result of the second test, and curve 23a and 23b show the result of a test in which a conventional wheel of uniform abrasive density was employed. For most purposes, if the edge of plate glass is formed with a-curve struck by a radius of between 3.5 and 6 mm, it is considered safe. Those skilled in the art oftentimes refer to such curves with-the radius lengthpreceding the letter R; e.g., a curve of 6 mm as 6R and a curve 4 mm as 4R. In this testing the configuration of the abrading surface was begun at 3.5R and over 6R wasconsidered as unacceptable.

Shape of diamond wheel: NOTE 205"""D X 6" X 3.5" X 2" 100% diamond content refers to 44 carat content l abrasive diamond grains: 150 F l l f 'fl l bond (binding agent); bronze in I cm volume oi the bond in rotation number: 3000 rpm the dlamonl layer tester: glass chamfering machine (manufactured by Taiyo Seiki) thickness of glass plate: mm

rate of variation amount of ratio of diamond (mm) of grinding work diamond layer content 7r curvature done (length consumptions radius (R) m) (AzB) (actual measurement) Result A B 3.5 0 first 4.5 6,500 test 69 23 5.3 15,000 3:1 (curve 5.7 25,000 21) 6.0 34580 3.5 0 second 4.0 10,000 test 100 25 4.3 22.500 4:1 (curve 4.3 33000 22) 4.4 42.850 3.5 0 4.5 2500 prior 65 5.1 5,000 wheel throughout 6.0 11,950 3.5 I 1,950 4.5 15,000 dressing 52 19.000 5.8 242.80

The wheel used in the first test, represented by the curve 21 was equipped with the hardness ratio of 311; and the radius gradually increased up to the vicinity of 20,000 meters and thereafter showed no particular variation until a predetermined 6R came about at 34,580 meters. The curve 22 is a result of a test made on the basis of the result of the first test in the curve 21, in consideration of the rates of diamond content as seen in the Table. In this case, R remained within 4.4 until the lifetime of the wheel was exhausted and an amount of grinding work done was 42,850 meters in length. The curves 23a and 23b illustrate the result of a test on a conventional grinding wheel. A rapid increase to 6R occurred at 1 1,950 meters of machining. The R rapidly increasing even thereafter, so that grinding operation was stopped at 6R. After a redressing the same rapid growth in R was observed as before until the lifetime of the diamond layer came to an end at 5.8 R, when the total grinding work of 24,2 80 meters was obtained. The last is illustrated by curve 23b.

In FIG. 6b the plan ofa rectangular shape (a, b, c, d) is shown which has an area identical with an area of a curved vertical cross section as shown in FIG. 6a. The FIG. 6b dimensions are the same as the area of a length L of a circular are E and the width H of a neutral surface of the curved vertical cross-section of FIG. 6b. Therefore, its vertical cross-sectional area is equal to that of FIG. 6a. The circular are E of a radius R is drawn which passes each point of b, X, c in the rectangular vertical cross-section provided that X 18 the middle point. A design is formed of the dias having high hardness are initially on one side of circular arc curve B. The border is arranged at the symmetrical areas A,

A of the X-x and the dias having low hardness are arranged in the symmetrical areas B, B. As the total volume V of the diamond layer as initially designed is known, the depth Z of the distribution container 31 is upper and lower surface of the rectangular threedimensional container shown in the see-through perspective view of FIG. 7 are similar and have identical areas. The distribution container 31 is separated into A and B portions by means of a suitable thin partition wall plate which follows the arc E and the dias of proper hardness which correspond to said each portion are filled in the respective portions.

Now, the dias having variable hardness are mixed by taking arbitrary cross-sections which are in parallel with the line X-x and mixed, and how the hardness changes is obtained in each vertical cross-section as follows:

As shown in FIGS. 6 and 7, the line Xx is the centerline that divides into the rectangular cross section (a, b, c, d) and the circular are C. and when the surface including the line Xx is disposed perpendicularly toward the bottom surface, it can be seen that this partition 5 wall becomes the rectangular shaped area of XX'xx.

From this it can be seen that the crossing points of the arbitrarily differentiated cross section YYyy which is in parallel with the surface XXxx is represented by C0 S Cm SCn/S+ S =hCm +hCn (refer to FIG.

provided that the crossing points of the upper and lower surfaces of the distribution container 31 with the circular are E are at K, K points, and also the area of 35 the differentiated cross section YYdd' forming the portion A is at S and the rate of content of the dia is Cm percent, the area of differentiated cross section KKy'y forming the portion B is named S, the rate of content of the dia is named Cn percent, the average hardness 4C of the differentiated cross section YYyy is named C0 percent and wherein Cm Cn, the dias of the differentiated cross section from the ends a, b of the distribution container 31 toward the ends 11, c is inversely proportional with respect to the maximum hardness Cm at the time of the design and the height h of the circular are E and is reduced continuously gradually and becomes the minimum Cn over the center portion Xx and then is increased continuously gradually from that point and becomes again the maximum Cm at the dif- 5( ferentiated cross section d, c.

The upper surface of the distribution container 31 is a pattern which is redrawn in the rectangular shaped area whose cross section is identical with the dias of FIG. 60 as shown in FIGS. 6 and 7. Therefore, the

shape of the circular are El may be suitably drawn to 6( However, as the total volume V of the dias is initially determined, a depth Z of the distribution container 29 can be obtained as the value of a function of the rectangular area.

The distribution container 29 which is prepared in 6: accordance with the foregoing is disposed over the upper part of a funnel 32 of a shape shown in the perspective view of FIG. 8. The container moves in the direction of the arrow at a selected speed. When the dias automatically determined on the assumption that the reach the protruding lower lip of the funnel 32, they drop continuously sequentially in parallel with the line X-x in the form of differentiated cross-section from the bottom portion of the distribution container 29. The dropping dias are completely mixed by means of a suitable rnixing device 33 and into the mold M. The molding parts 34, 35 and 36 for the diamond wheel are rotated. The dropped dias become the deposited layer whose originally designed hardness continuously changes, and the deposited layer dias are maintained in parallel with the bottom surface by means of a suitable leveler plate or tab 38. The deposited layer of dias is molded by the press machine to the dimensions of FIG. 6a by using a pressure cover 39. After the molding is completed, the diamond wheel is completed through a suitable manufacturing process such as sintering.

In the structure of the mold, reference numeral 34 is an outer ring frame forming the curved vertical crosssection of the dias which corresponds to an outer periphery of the wheel having a radius of curvature R of FIG. 60. Part 35 is its inner ring type frame and 36 is a cradle for supporting the ring frames and dias. These components are conveniently assembled so that the dias when molded, can be removed. The mold is disposed on a rotating platform 37. Reference numeral 39 indicates the pressure cover for press molding the deposited layered dias into the correct dimensions.

The dias can be fed to the hopper from container 31 by several convenient methods. One method is to have a slidable bottom 31. As container 29 is moved forwardly, the dias will be fed to the hopper 32 if the bottom is anchored. The rate of movement of container is coordinated with the rotation rate of the mold.

In a general manner, while there has been disclosed an effective and efficient embodiment of the invention, it should be well understood that the invention is not limited to such an embodiment as there might be changes made in the arrangement, disposition, and form of the parts without departing from the principle of the present invention.

I claim:

1. A grinding wheel for forming a generally convex peripheral surface from a generally flat peripheral surface in a glass plate whereby the amount of materials that have to be ground away from the generally fiat peripheral surface varies from a minimum at the center of the peripheral surface to a maximum at its edges,

a generally concave grinding layer of a selected thickness disposed about the periphery of said wheel and having a shape the complement of that to be imparted to said flat peripheral surface,

said layer being comprised of a binder and diamond particles and the amount of said diamond particles varying uniformly and evenly in distribution throughout said thickness from a minimum concentration at the center of said concave surface to a maximum at its edges and in proportion to the amount of materials that have to be ground away from said flat peripheral surface to form said convex peripheral surface.

2. The grinding wheel of claim 1 wherein said concave grinding layer is V-shaped. =l 

1. A grinding wheel for forming a generally convex peripheral surface from a generally flat peripheral surface in a glass plate whereby the amount of materials that have to be ground away from the generally flat peripheral surface varies from a minimum at the center of the peripheral surface to a maximum at its edges, a generally concave grinding layer of a selected thickness disposed about the periphery of said wheel and having a shape the complement of that to be imparted to said flat peripheral surface, said layer being comprised of a binder and diamond particles and the amount of said diamond particles varying uniformly and evenly in distribution throughout said thickness from a minimum concentration at the center of said concave surface to a maximum at its edges and in proportion to the amount of materials that have to be ground away from said flat peripheral surface to form said convex peripheral surface.
 2. The grinding wheel of claim 1 wherein said concave grinding layer is ''''V''''-shaped. 